Easy Front end Alignment
Toe in alignment for the MGB should be between 1/16 and 1/8 of an inch. The general purpose of toe in is to prevent toe out. Toe out can cause the steering to become darty and unstable. Toe in stabilizes the steering but increased toe in increases tire wear. This is the short version of course but suffice to say the ideal toe in amount is just enough that the slop in the steering components (such as ball joints) do not create enough slop to ever cause Toe Out. So if your suspension is new you may want to lean toward 1/16". If your suspension is sloppy and worn you may want to lean toward 1/8".
First I like to raise the lower a-arm just enough to get the tire off the ground. You must lift from the a-arm. If you lift anywhere else the suspension will change position and the values will be irrelevant.
Measuring toe in using tire tread is extremely inaccurate. Measurements must be taken from the rim. I use laser levels from Harbor Freight for my front end alignment. I tie wrap the level so it sits on the rim (not the tire) in the same spot front and back. The laser itself actually sits out a little from the rim and it clears the fender and rear tires. I also have 15" rims. If the laser does not sit on the rim or if the laser does not clear rear rims just tape a shim to the laser so it does.
Harbor Freight Laser
By extending the measurements out you increase the accuracy. I measure out 11 feet. You must measure both in front of the car and behind the car. Measure the rear, rotate the tire, level the laser then measure the front. By averaging these values you come up with an accurate toe in. If you only go by the front value it will only be as accurate as the mounting of your laser. Measuring both front and rear values remove the mounting errors of the laser.
Also keep in mind the laser must be level. You can check this with the level on the laser or you can measure the height of the laser at the laser and at further out to make sure the height of the laser is the same.
To measure the distance use a angle. Put the dot right on the edge and mark the floor. If you mark the floor more then once (and you will), either erase the first marks or identify the marks as #2, #3 and so on. The marks can get confusing pretty quickly.
So you measured the distance at 11 feet both front and back. Lets say you measured 63.5" in the rear and 52.5" in the front. Now take the difference and divide it in two. The difference is 11 inches. Divided by 11 is 1" toe out.
This is a real easy and accurate process. I just made some camber changes to the car and had to re-align toe in. The whole process took me less than 30 minutes.